The invention relates to the field of natural products for use in treating tumors, especially pancreatic beta cell tumors, often referred to as insulinomas. More particularly, the invention concerns compounds obtainable from Banyan tree bark which are effective with regard to malignant and benign tumors characterized by pancreatic xcex2 cell transformations.
It is well understood that current therapies designed for the control and treatment of tumors in general, and malignant tumors in particular, are less than satisfactory. The hammer-fisted approaches of surgery, chemotherapy and radiotherapy are clearly unfocused and accompanied by unpleasant, and often quite serious, side effects as well as being characterized by limited effectiveness. Other treatment methods based on natural products are currently in use (Lee, K. H., Med. Res. Rev. (1999) 19:569-596) and others are in clinical trials (Levya, A., et al., Anticancer Res. (2000) 20:1029-1031). These remedies, while they may be effective in particular instances, can hardly be considered to solve the overall problem.
The present invention provides a plant derived agent which is focused on the treatment of tumors of particular origins, most prominently those which can be characterized as insulinomas. The new derivative is also cytotoxic to additional cell lines which presage its use in treatment of tumors with characteristics analogous to these cell lines. It is not cytotoxic to others, indicating a specificity of effectiveness that is advantageous in designing targeted treatments.
Pancreatic endocrine tumors, in general, secrete excess amounts of hormones and can be classified as insulinomas, gastrinomas, VIPomas, glucagonomas, and somatostatinomas, for example, by virtue of the nature of the hormones they secrete (Jonathan, C., et al., Cur. Opin. Oncol. (2001) 13:52-56). Insulinoma is a very common type, although it is more common in small domestic animals than in humans. Insulinomas are characterized by hypoglycemia and hyperinsulinism, and have the consequence of neuroglycopenia in humans. Behavioral changes often accompany these tumors, both in small animals (such as ferrets) and in humans.
Treatment of insulinomas specifically has focused on surgery (although localization is often difficult) and the use of certain compounds, including dizoxide (Gill, G. V., et al., Postgrad. Med. J. (1997) 73:640-641); streptozotocin and doxorubicin (Philippe, R., et al., Digestion (2000) 62:73-78); and analogs of somatostatin (Arnold, R., et al., Digestion (2000) 62 Supp. 1:84-91). An additional herbal medication has been used in ferrets (Bodofsky, D., www.newrainbowbridge.com).
Of particular interest is the use of somatostatin as this compound (a cyclic 14 amino acid peptide) exhibits antiproliferative and antisecretory effects in endocrine tissues. Analogs of somatostatin, such as octreotide and lanrcotide are typical of the redesigned somatostatin compounds currently in use in antitumor treatment. However, as it is known that somatostatin exerts its effects through interaction with G-protein coupled plasma membrane receptors, and such receptors are only present in approximately 50% of insulinomas, the effectiveness of these treatments is limited.
Other compounds of plant origin which are useful in antitumor treatment include dactinomycin, bleomycin, vinblastine, irinotecan, topotecan, etoposide, and paclitaxel. The compounds useful in this regard include a multiplicity of categories, including lectins, polyphenolic compounds, sesquiterpene lactones, alkaloids, polysaccharides, anthracenediones, tannins, lignans, quassinoids, triterpene glucosides, flavanoids, colchicine derivatives, and quinone derivatives (see, for example, Cragg, G. M., Seminar Oncol. (1997) 24:156-163; Cragg, G. M., et al., Ciba Found Symp. (19994) 185:190-196; Jose, M., et al., J. Med. Chem. (2001) 44:1257-1267.)
A number of compounds have been isolated from the bark of Ficus bengalensis (Banyan tree). Isolation of a compound that improves glucose tolerance in alloxan-diabetic rabbits has been reported by the present inventor Babu, B. V., et al., Thesis submitted to University of New Delhi (Dec. 1985); Babu, B. V., et al., Ind. J. Biochem. Biophys. (1988) 6:714-718. Two flavanoid glycosides, the 5,3xe2x80x2 dimethyl ether of leucocyanidin-3-o-xcex2-galactosyl cellobioside and the 5,7-dimethyl ether of leucopelargonidin-3-o-xcex1-L rhamnoside have been shown to produce hypoglycemic (antidiabetic) affects in experimental animals. See Kumar, R. V., et al., Ind. J. Biochem. Biophys. (1989) 26:400-404; Augusti, K. T., Ind. J. Physiol. Pharmacol. (1975) 19:218-220; Augusti, K. T., et al., Ind. J. Med. Res. (1994) 99:82-86. Antioxidant effects of these compounds have also been shown in hyperlipidemic rats (Daniel, R. S., et al., Ind. J. Exp. Biol. (1998) 9:902-906).
It has now been found that in addition to the compounds of the foregoing effects, a preparation from Banyan bark exhibits insulin antisecretory activity and is cytotoxic to specific target cells.
The invention provides a method to isolate a composition from Banyan bark which exhibits a characteristic spectrum of cytotoxicity with respect to cells important in the development of tumors, especially those of the pancreas and kidney. The isolated composition is useful in treatment of tumors characterized by these cells and in inhibiting the production of insulin.
Thus, in one aspect, the invention is directed to a method to isolate a composition which inhibits insulin secretion in xcex2TC-6 cells and HIT-T15 and is non-cytotoxic to xcex2TC-6 cells and
cytotoxic to HIT-T15 cells; is cytotoxic to the non-insulin secretory cell line SV40 Mes13 cells, but not cytotoxic to the non-insulin secretory cell line MDCK cells.
The Method Comprises
a) extracting the bark of Ficus bengalensis with a solvent of lower alcohols to obtain an extract;
b) drying the extract to obtain a residue;
c) dissolving the residue in methanol;
d) loading the dissolved residue onto an activated silica gel column;
e) eluting the column with additional ethanol:hexane (2:1) to obtain an eluent; and
f) removing solvent from the eluent to obtain said composition.
In another aspect, the invention is directed to a composition having the aforesaid characteristics which is obtainable by the method described. In still another aspect, the invention is directed to methods to treat tumors, especially of the pancreas which method comprises administering to a subject in need of such treatment an effective amount of the composition of the described characteristics. In still another aspect, the invention is directed to a method to inhibit insulin secretion using this composition.